1. Technical Field of the Invention
The present invention relates to a rotary compressor having a piston integrated with a blade, a refrigerating cycle of a refrigerating apparatus, an air conditioning apparatus, or the like using the compressor, and a refrigerator using the compressor.
2. Description of the Conventional Art
FIGS. 5 and 6 show a conventional rolling piston type rotary compressor (2-cylinder rotary compressor in the example) disclosed in, for example, Patent Publication No. 2502756. FIG. 5 is a longitudinal cross section of the rotary compressor and shows a refrigerating cycle. FIG. 6 is a transverse cross section of a compression mechanism portion of the rotary compressor. The description will be given hereinafter with reference to FIGS. 5 and 6. The conventional rotary compressor comprises an electric motor portion 50 having a stator 1 and a rotor 2 and a compression mechanism portion 60 which is driven by the electric motor portion 50 and has a frame 19, a cylinder 5 having a cylinder chamber 4 to which a suction port 3 and a discharge port (not shown) are opened, a partition panel 34 for partitioning the cylinder into two chambers, a cylinder head 20, a piston 8 rotatably fit on an eccentric shaft portion 7 of a driving shaft 6 and disposed in the cylinder 5, a vane 11 for partitioning the cylinder chamber 4 into a low pressure chamber 9 communicating with the suction port 3 and a high-pressure chamber 10 communicating with the discharge port (not shown), a vane spring 12 for urging the vane 11 against the piston side so that the valve 11 is not to be apart from the piston 8, and the driving shaft 6. The electric motor portion 50 and the compression mechanism portion 60 are directly mounted in a hermetic vessel 13 in which a discharge pressure atmosphere or a suction pressure atmosphere is kept, by means of welding, shrinkage fitting, or the like. FIG. 5 shows the case of using the discharge pressure atmosphere. The operation is performed in such a manner that the piston 8 revolves along the inner wall of the cylinder chamber 4 according to the rotation of the driving shaft 6, a compressible fluid such as a refrigerant gas sucked from the suction port 3 is compressed in association with the revolution, and the fluid is discharged from the discharge port (not shown).
FIG. 7 is a longitudinal cross section of a conventional blade-integrated piston type rotary compressor disclosed in, for example, Japanese Unexamined Patent Publication No. 10-047278 and FIG. 8 is a transverse cross section of a compression mechanism portion of the rotary compressor. In FIGS. 7 and 8, the compressor is comprised of an electric motor portion 50 having a stator 1 and a rotor 2 and a compression mechanism portion 60 driven by the electronic motor portion 50. The electric motor portion 50 and the compression mechanism portion 60 are housed in a hermetic vessel 13.
The compression mechanism portion 60 comprises a frame 19, a cylinder 5 having a cylinder chamber 4 to which a suction port 3 and a discharge port 14 are opened, a cylinder head 20, a piston 15a which is rotatably fit on an eccentric shaft portion 7 of a driving shaft 6 and disposed in the cylinder 5, a blade 15b provided integrally with the piston 15a, for partitioning the cylinder chamber 4 into a low pressure chamber 9 communicating with the suction port 3 and a high pressure chamber 10 communicating with the discharge port 14, a guide 17 which is rotatably fit in a cylindrical bore 16 formed in the cylinder 5 and slidably and swingably support the blade 15b and a driving shaft 6.
By the rotation of the driving shaft 6, the piston 15a revolves along the inner wall of the cylinder chamber 4 so as to swing as a fulcrum via the blade 15b on a rotation center 18 of the guide 17, the compressible fluid such as refrigerant gas sucked from the suction port 3 is compressed every revolution, and the fluid is discharged via the discharge port 14.
A structure similar to the blade-integrated piston type rotary compressor in which the piston and the blade are integrally formed and piston revolves eccentrically in the cylinder with aid of swinging motion is disclosed in FIG. 373 in page B5-159 and explanation for it in "Mechanical Engineer's Handbook" (issued by The Japan Society of Mechanical Engineers, Apr. 15, 1987).
In the conventional blade-integrated piston type rotary compressor, the electric motor portion 50 and the compression mechanism portion 60 are fixed in the hermetic vessel 13 by means of shrinkage fitting, welding, or the like and the discharge pressure atmosphere is kept in the hermetic vessel 13.
In the conventional rolling piston type rotary compressor, as described above, the compression mechanism portion comprises the cylinder 5, the piston 8, the vane 11, and the vane spring 12. In order to partition the cylinder space into the low pressure chamber 9 communicating with the suction port 3 and the high pressure chamber 10 communicating with the discharge port 14 by the piston 8 and the vane 11, it is necessary to make the tip of the vane 11 and the peripheral surface of the piston 8 always come into contact with each other with a right force. When the discharge pressure atmosphere is kept in the hermetic vessel 13, a force by the differential pressure between the compression chambers 9 and 10 and the hermetic vessel 13 acts in the direction of urging the vane 11 against the piston 8, so that the vane 11 can be pressed against the piston 8 by using the differential pressure. It is therefore sufficient to set the pressing force of the vane spring 12 to a smaller value by taking use of the differential pressure into account. In this case, in the compressor just before starting, a pressure is in a balanced state. Since the vane 11 is pressed against the piston 8 with a force which is smaller than the pressing force necessary in a steady operation by an amount of the differential pressure, an excessive load is not applied on the piston 8 and stable starting can be performed by a motor having the minimum starting torque.
On the contrary, during an off period of an ON/OFF operation performed by, for example, a compressor for refrigerator, the high-temperature high-pressure gas refrigerant in the hermetic vessel 13 is leaks from each of a contact surface 21 between the cylinder 5 and a frame 19, a contact surface 23 between the cylinder 5 and a cylinder head 20, and a contact surface 35 between the cylinder 5 and the partition panel 34 to the low pressure chamber 9 and a suction pipe 24 due to the pressure difference since the suction pressure is kept in a portion of the suction pipe 24, the suction port 3 and the low pressure chamber 9 in the cylinder 5 and the other portion in the hermetic vessel 13 is filled with the discharge pressure atmosphere. The leaking gas flows back from the suction pipe 24 to an evaporator 36 and a temperature rise tends to be caused in a condenser of a refrigerator or the like. In order to prevent this, a check valve or the like has to be installed between the suction pipe 24 and the evaporator 36, so that a problem of increased cost arises.
On the other hand, in case of using the structure such that the suction pressure atmosphere is kept in the hermetic vessel, the discharge pressure is kept in a portion of the high pressure chamber, the discharge portion, and the discharge pipe in the hermetic vessel and the other portion of the hermetic vessel is filled with the suction pressure atmosphere. A discharge valve provided on the discharge pipe side of the discharge port, however, plays the role of a check valve and separates the high-temperature high-pressure gas from the other. A leakage into the suction pressure portion does not occur during the off period of the ON/OFF operation and a gas does not flow back to the evaporator without providing the circuit with a check valve or the like.
When the rotary compressor has the construction such that the suction pressure atmosphere is kept in the hermetic vessel 13, a force by a differential pressure between the compression chamber and the hermetic vessel 13 is applied on the vane 11 in the direction of separating the vane 11 from the piston 8. It is therefore necessary to set a pressing force of the vane spring 12 for pressing the vane 11 against the piston 8 to a larger value by an amount of the maximum differential pressure within an assumable operation range, and the vane spring 12 having a pressing force larger than that in the case where the discharge pressure atmosphere is kept in the hermetic vessel 13. In a pressure balanced state just before starting, the pressing force of the vane spring 12 is not cancelled out by the differential pressure but is applied as it is, so that the vane 11 is pressed against the piston 8 by the force larger than the pressing force necessary during the steady operation. An excessive load is accordingly applied on the piston 8 and a motor having a large starting torque is necessary for starting.
When the motor is designed so as to have a large starting torque, the motor efficiency at the time of steady operation is sacrificed and the performance of the compressor therefore deteriorates. Since the pressing force of the vane spring is set to the maximum value within an assumable operating range, the vane cannot be pressed according to operating conditions (difference between suction and discharge pressures). Since the pressing force is always strong, the sliding condition between the tip of the vane and the peripheral surface of the piston is severe. The severe sliding condition causes not only wear of the vane tip but generation of sludge. Since such a construction that the suction pressure atmosphere is kept in the hermetic vessel is employed, there is such an inconvenience that generated sludge is exhausted through the discharge pipe to a circuit without being captured in the space in the hermetic vessel, and accumulated in the circuit to close a capillary tube.
In case of using HFC refrigerant such as R134, even if the discharge pressure atmosphere is kept in the hermetic vessel and the pressing force of the vane is reduced, an extreme-pressure effect as produced with a CFC refrigerant cannot be expected because of no chlorine atoms contained in the HFC refrigerant. The lubricity of the sliding portion consequently deteriorates and the sliding condition between the tip of the vane and the peripheral surface of the piston becomes severe.
On the other hand, according to the conventional blade-integrated piston type rotary compressor, the discharge pressure atmosphere is kept in the hermetic vessel 13 and the blade portion 15b corresponding to the vane is formed integrally with the piston 15a. Consequently, the pressing force is not applied on the piston 15a at the time of starting, stable starting can be always performed without setting the starting torque of the motor to an excessive value, and there is no inconvenience such as wear and sludge stack due to the sliding of the tip of the vane.
On the contrary, since the construction such that the discharge pressure atmosphere is kept in the hermetic vessel is used, in a manner similar to the rolling piston type rotary compressor using the discharge pressure atmosphere, the high-temperature high-pressure gas refrigerant in the hermetic vessel 13 flows back during an off period of operation from the high-pressure hermetic vessel 13 to the compression chamber, the suction pipe 24, and the evaporator 36 having a lower pressure through the contact surface 21 between the cylinder 5 and the frame 19 and the contact surface 23 between the cylinder 5 and the cylinder head 20 to raise the temperature of a condenser of a refrigerator or the like. Consequently, in order to prevent this, a check valve or the like has to be provided in a circuit between the suction pipe 24 and the evaporator 36 and there is a problem of increased cost.
When the compression mechanism portion and the electric motor portion are elastically supported in the hermetic vessel and a clearance is provided between both of the compression mechanism portion and the electric motor portion and the hermetic vessel inner wall, it is necessary to isolate and seal a portion between a pipe attached to the hermetic vessel and the compression mechanism portion on either of the discharge side or the suction side. In the case where the discharge pressure atmosphere is kept in the hermetic vessel, the suction pipe attached to the hermetic vessel is laid in the hermetic vessel, so that the portion of the suction pipe attached to the hermetic vessel and the suction port of the compression mechanism portion cylinder is sealed from the discharge pressure in the hermetic vessel so as to maintain the suction pressure. In the case where the suction pressure atmosphere is kept in the hermetic vessel, it is also necessary to lay the discharge pipe attached to the hermetic vessel so as to maintain the discharge pressure by sealing the portion between the discharge pipe and the discharge port of the compression mechanism portion cylinder. The pipe laid in the hermetic vessel has to be designed with low rigidity so as not to be deformed, fatigued, or damaged by the vibration of the compression mechanism portion and the electronic motor portion which are elastically supported in the hermetic vessel. Since the volume flow rate of gas in the suction pipe portion through which gas before compression flows is higher than that in the discharge pipe portion through which compressed gas flows and the flow velocity of the gas in the suction pipe portion is faster than that in the discharge pipe portion, the pipe diameter of the suction pipe portion cannot be reduced from the viewpoint of pressure loss. It cannot be therefore said that the laying of the suction pipe is a realistic choice. That is, when the electric motor portion is elastically supported in the hermetic vessel and the discharge pressure atmosphere is kept in the hermetic vessel, such a problem is caused that the pressure loss in the suction pipe laid in the hermetic vessel becomes large in order to prevent deformation and damage.
Therefore, the electric motor portion 50 and the compression mechanism portion 60 are directly attached to the hermetic vessel 13 in the construction where the discharge pressure atmosphere is kept in the hermetic vessel. As a result, vibration and noise in the compressor are directly transmitted to the outside so that low vibration and low noise cannot be always achieved. In order to reduce the vibration transmitted from the compressor to the piping system constructing a refrigerating cycle of a refrigerator or the like and to prevent the pipe from being damaged due to deformation caused by the transmitted vibration, it is necessary to form the piping to the compressor with a small diameter and a long movable portion. As a result, the efficiency is reduced by the pressure loss, costs are increased due to complication of the piping and, further, the piping design becomes complicated.
Moreover, when the discharge pressure atmosphere is kept in the hermetic vessel 13, the force by the differential pressure applied on the guide 17 is applied concentratedly on a narrow flat sliding portion between the guide 17 and the blade 15b. The sliding loss therefore increases and the reliability deteriorates.
Irrespective whether the vane (blade) is integral with the piston or not, the space 5a in which the vane (blade) moves is generally opened in the space in the hermetic vessel 13 as shown in FIG. 9A and the pressure therein is usually equalized. When the space is sealed as shown in FIG. 9B, the vane (blade) goes in and out from the closed space 5a. Since an increased or decreased space volume due to the movement of the vane (blade) causes a loss, it is preferable to open the space 5a to the space in the hermetic vessel 13 irrespective whether the discharge pressure atmosphere or the suction pressure atmosphere is kept in the hermetic vessel 13.
In the case of using a blade-integrated type 2-cylinder construction, increase or decrease of volume in the space 5a in which two blades move is cancelled out. Although it is therefore possible not to open the space 5a to the hermetic vessel, there is a problem that the behavior of the guide becomes unstable. As shown in FIGS. 10A and 10B, the curvature of the cylindrical surface of the guide 17 and the curvature of the cylindrical bore portion 16 in which the guide is fit are not equal and have to have a small curvature difference from the viewpoint of assembling performance, slidability, and the like. A supporting point S at which the guide 17 comes into contact with the cylindrical bore is determined by the balance of forces applied to the guide 17. When the space 5a in which the blade moves is not opened to the hermetic vessel, the pressure in the space is equal to an intermediate pressure Pm between a suction pressure Ps and a discharge pressure Pd due to the leakage between the compression chambers 9 and 10. The supporting point of the guide on the discharge side is a point near the inner circumference of the cylinder as shown in FIG. 10A when the pressure Pc in the high pressure chamber 10 is lower than Pm. When the compression develops and the pressure Pc in the high pressure chamber 10 increases to a value higher than Pm, the supporting point comes to a point near the blade moving space as shown in FIG. 10B. As mentioned above, since the supporting point is not fixed and becomes unstable at the moment when the supporting point is moving between the state of FIG. 10A and the state of FIG. 10B, there is a problem of slidability and reliability of the guide 17.
When the blade moving space 5a is opened to the hermetic vessel 13, both of the loss due to the increase or decrease of volume in the blade moving space and the instability of the guide supporting point can be avoided. When the hermetic vessel 13 has therein the discharge pressure, as shown in FIG. 11, the pressure in the blade moving space 5a becomes the discharge pressure Pd, supporting points S and S' of the guide 17 are near the cylinder inner circumference and loads F.sub.3 and F.sub.3 ' between flat portions of the guide and side surfaces of the blade are applied concentratedly to a narrow portion near the cylinder inner circumference, so that the sliding loss increases and the reliability deteriorates.
Further, in the case where the discharge pressure atmosphere is kept in the hermetic vessel 13, the discharge pressure portion in the circuit volume during the operation increases corresponding to an increased space with high pressure in the hermetic vessel and an oil stored in the hermetic vessel is exposed to the discharge pressure, so that the amount of refrigerant dissolved in the oil increases more than that in the suction pressure atmosphere, and the amount of refrigerant enclosed in the circuit increases consequently. It is therefore undesirable from the viewpoint of safety from catching fire and explosion to use a combustible refrigerant such as hydrocarbon refrigerant (HC refrigerant). From the viewpoint of suppressing the enclosed refrigerant amount, it is desirable that the space volume in the hermetic vessel is as small as possible. However, in the reciprocating type compressor in which the suction pressure atmosphere is kept in the hermetic vessel, as shown in FIG. 12, since the piston 15a and the cylinder 5 are disposed on only one side with respect to the center of the motors 1 and 2 and the driving shaft 6 and the construction is asymmetrical, the section having no compression mechanism portion causes increase of the space volume.